A prominent means of lighting long store-shelves is the fluorescent lamp, due to its low cost and good luminous efficacy. While the linear geometry of this lamp is appropriate for long shelves, its isotropic radiation pattern is not, because most of the light misses the target, unless bulky and expensive reflectors are employed. Also, the light that does make it to the shelf is not at all uniform.
As their prices continue to fall, linear arrays of light-emitting diodes (LEDs) are becoming a viable alternative to fluorescent lamps, due to their longer life and greater compactness. Because LEDs radiate into a hemisphere (or less), optical lensing can be employed to distribute their light output. Such optics can be mounted individually on the LEDs, typically as domes. The prior art is deficient, however, in providing linear lenses for long arrays of LEDs. Linear, or cylindrical lenses, are preferred for linear arrays because of the low cost of extruding the lenses in a transparent plastic such as acrylic.
Low-cost LEDs can be economically provided on low-voltage tapes, spaced every 10-20 mm, such as those sold by the Osram Corporation under the ‘Linear Flex’ product line. Provision as tape reels enable automated production to install lengths of such LED tapes into long extruded brackets, onto which long extruded lenses can be mounted over the tape's line of LEDs. Extruded lenses, with their constant cross section, fall in the province of cylindrical lenses, also known as rod lenses, but the prior art thereof has been concerned more with imaging than with illumination, particularly in such devices as scanners and copiers.
Thus there is a need for cylindrical lenses designed for illumination by LEDs, particularly designs that will produce uniform illumination on nearby flat surfaces.
The present invention will remedy the current lack of suitable optics for uniform-illuminance LED shelf-lights, and in particular will provide numerous preferred embodiments for different illumination geometries.